Transcortin will be treated with cyanogen bromide and the resulting peptide isolated by ion-exchange chromatography. The carbohydrate and amino acid composition of each will be determined. Another batch of transcortin will be affinity-labeled with 17-(5'-oxo-6'-diazohexanoyloxy)-4-pregnene-3,20-dione and then treated with cyanogen bromide. Isolation of the peptides will tell us which one is located at or near the binding site. Other experiments will identify the number of carbohydrate chains present and their role, if any, in binding of cortisol and progesterone.